const Int_t N = 20;
Int_t theN = 1;

Double_t x[N];
Double_t y[N];

double mean = 1.0;
double sig  = 0.2;

void ml_add_data()
{

  TF1* f = new TF1( "f", loglike, 0, 2, 1 );
  f->SetParameter( 0, sig );
  f->Draw();
  f->SetTitle( "-ln(L) for Gaussian" );
  f->GetXaxis()->SetTitle( "x" );
  f->GetYaxis()->SetTitle( "-ln(L)" );
  Double_t xmin = f->GetMinimumX();
  Double_t ymin = f->GetMinimum();

  for( Int_t i = 0; i < N; ++i ) {
    x[i] = gRandom->Gaus( mean, sig );
    theN = i+1;
    f->Draw();

    TGraph* g = new TGraph( N, x, y );
    g->SetMarkerStyle( 20 );
    g->SetMarkerSize( 1.0 );
    g->Draw( "p" );

    gPad->Update();
    char bla[80];
    getline(cin,bla);
  }



  return;

}

Double_t loglike( Double_t* input, Double_t* par )
{
  Double_t mymean = input[0];
  Double_t mysig  = par[0]; 
  
  Double_t val = theN * log( sqrt( 2*TMath::Pi() ) * mysig );
  for( UInt_t i = 0; i < theN; ++i ) {
    Double_t arg = ( x[i] - mymean ) / mysig;
    val += 0.5*arg*arg;
  }

  return val;
}